1. Technical Field of the Invention
The present invention relates to an AC (alternating current) generator, and in particular, to an automotive AC generator with a rectifier capable of rectifying generated AC power into DC (direct current) power.
2. Description of Related Art
In a recent automotive vehicle, an effective capacity inside the passenger compartment has been desired to be larger. In realizing such an object, one countermeasure is to reduce the space of the engine room. It is also required that an automotive AC generator be downsized.
Under such circumstances, a significant subject to be resolved is that the cooling performance of a rectifier mounted to the automotive AC generator is maintained or improved. This subject is not an easy matter, because saving the space in the engine room will lead to deteriorated temperature environment therein and downsizing the automotive AC generator itself will lead to deterioration in the cooling efficiency thereof.
FIG. 10 shows an automotive AC generator according to a first conventional example. This generator adopts a configuration for improving the cooling efficiency, in which both of positive and negative fins 101 and 102 on which rectifying elements 100 are mounted are arranged, in an overlaid fashion, in parallel to each other in an axial direction thereof. A protective cover 103 has two cooling air inlets 104 opened at predetermined portions near the rectifying elements 100. Cooling air is thus directly introduced to the rectifying elements 100 (precisely, to the back surfaces of the fins 101 and 102) are cooled down by the introduced cooling air.
However, the above first conventional example has an inconvenience, which is concerned with the circulation of the cooling air. To be specific, the cooling air that has been introduced is directly blown onto a predetermined region on each of the backs of the cooling fins 101 and 102, such a region almost corresponding to each of the positions of the rectifying elements 100 or thereabout. But the cooling air is reluctant to circulating around each of the cooling fins 101 and 102 toward the surface on which element connection terminals are located thereon, respectively. In addition, one rectifying element located outward in the radial direction is placed in the downstream flow of the cooling air that passes by the other rectifying elements. Thus, it is obliged that the rectifying elements located radially outward are cooled down by the cooling air of which temperature has already been raised considerably. Therefore, the above cooling configuration has faced the problem that the cooling efficiency was not sufficient.
In consideration of the above inconvenience, the present applicant has already provided a second conventional example according to Japanese Patent Laid-open publication No. 11(1999)-164538, which is typically shown in FIGS. 11 and 12. This example concerns an automotive AC generator that has a larger-diameter fin 503 located near to a rear frame 3b and a smaller-diameter fin 501 located near to a protective cover 8. Rectifying elements 502 and 504 are arranged on the fins 501 and 503, respectively, in the axial direction of the generator. The rectifying elements 502 and 504 come face to face with each other with a predetermined gap left therebetween, but both the fins 501 and 503 are mutually shifted outward or inward in the radial direction. The protective cover 8 has axial openings 801, each of which permits air to pass therethrough directly to each positive rectifying element 502. Additionally, there is formed a radial air passage 801 between the larger-diameter fin 503 and the rear frame 3b in such a manner that the air passage 801 passes by the central position of each of the negative rectifying elements 504. A radial opening 802 that allows air to be directly introduced to one end of the radial air passage 810 that is located outward in the radial direction. This cooling configuration causes the cooling air to circulate the gap between both the element-mounting surfaces of the fins 501 and 503. Hence the cooling air that has been taken in passes along the surfaces of the cooling fins 501 and 503 on which the rectifying elements 502 and 504 are disposed, respectively.
In the above automotive AC generator according to the second conventional example, however, there is still a problem that the larger-diameter fin 503 may suffer from a shortage of the cooling capacity, although the radial air passage 810 allows the cooling air to pass along the frontal and rear surfaces of the larger-diameter fin 503. Practically, if the amount of flow of air from a cooling fan 21 is reduced on account of, for example, making the entire size of the automotive AC generator compact, the amount of flow of cooling air that passes the radial air passage 810 formed between the rear frame 3b and the larger-diameter fin 503 is also reduced. In such an occasion, the cooling performance for the larger-diameter fin 503 will decrease, with the result that the rectifying elements 504 secured on the larger-diameter fin 503 are subjected to a rise in its temperature.
The present invention has been performed in consideration of the above-described drawback, and an object of the present invention is to provide an automotive AC generator with a rectifier including a larger-diameter fin, which is able to provide the larger-diameter fin with cooling air in a more effective way so that the cooling performance of the larger-diameter fin is increased dramatically.
In order to achieve the above object, the present invention provides a vehicle AC generator comprising: a frame, having a radial direction and an axial direction, formed to have an inner wall area, a radially inner end, and a radially outer end in the radial direction and an outer end portion in the axial direction; a stator secured on the inner wall area of the frame; a rotor rotatably supported at the frame; a rectifier including a plurality of rectifying elements and being secured on the outer end portion of the frame, said plurality of rectifying elements being classified into a first group of rectifying elements and a second group of rectifying elements; a protective cover having an inner end portion and being secured on the outer end portion of the frame to cover the rectifier; and a cooling fan secured at the rotator and configured to take in cooling air from one side on which the rectifier is located. The rectifier comprises a larger-diameter fin disposed to extend in the radial direction with facing the outer end portion of the frame, said larger-diameter fin serving as both of a cooling member for the first group of rectifying elements and a connecting conductive member of the first group of rectifying elements mounted on the larger-diameter fin; and a smaller-diameter fin disposed to face the inner end portion of the protective cover, said smaller-diameter fin serving as both of another cooling member for the second group of rectifying elements and another connecting conductive member of the second group of rectifying elements mounted on the larger-diameter fin. The protective cover comprises an axial opening facing the smaller-diameter fin and being formed through the frame to take cooling air in. The frame comprises a radial opening formed with the aid of the radially outer end of the frame to take cooling air in, a radial air passage formed with facing the larger-diameter fin and formed to circulate the cooling air taken in through the radial opening along the larger-diameter fin inwardly in the radial direction, and a plurality of grooves each positionally corresponding to a mounted position of each rectifying element on the larger-diameter fin and being formed on the radial air passage to connect the radially outer end and the radially inner end of the frame.
Accordingly, the cooling air taken in through the radial opening is able to cool down the larger-diameter fin. That is, the cooling air that has taken in from the outside circulates through the radial air passage toward radially inward with the air along the larger-diameter fin. The larger-diameter fin can therefore be cooled down effectively by the cooling air whose temperature is lower, which gives a preferable cooling operation to the rectifying elements mounted on the larger-diameter fin.
In addition, the frame has the radial air passage on which the grooves are formed radially therethrough correspondingly to each of the mounted positions of the rectifying elements on the larger-diameter. Hence a large amount of cooling air is able to circulate along each groove, thereby cooling down the mounted positions of the larger-diameter fin in a surer and steadier manner.
On the other hand, the smaller-diameter fin is preferably cooled down by lower-temperature cooling air taken in through the axial opening from the outside. In response to such cooling, the rectifying elements mounted on the smaller-diameter fin are also cooled down effectively.
The existence of the grooves on the radial air passage leads to only partial enlargement in the section of the radial air passage itself. In other words, an amount of cooling air that circulates through the entire radial air passage is avoided from increasing to a larger extent. Hence an amount of cooling air to be taken in through the axial opening is also less, almost completely eliminating the worry that the cooling performance for both of the smaller-diameter fin and the rectifying elements mounted thereon may reduce.
In the foregoing fundamental configuration, it is preferred that each groove has a width set to an amount equal to or larger than about 0.5 times a width of each rectifying element mounted on the larger-diameter fin.
This limitation of the dimensions is also effective in obtaining a steadier cooling performance on the larger-diameter fin and the rectifying elements mounted thereon. This is because such limited dimensions makes it possible to give a sufficient amount of air to the cooling air that passes along the back of each of the mounted positions of the rectifying elements on the front of the larger-diameter fin.
It is still preferred that each groove has a width set to an amount equal to or smaller than about 1.5 times a width of each rectifying element mounted on the larger-diameter fin.
This limitation of the dimensions is also effective in obtaining a steadier cooling performance on the smaller-diameter fin and the rectifying elements mounted thereon. This is because such limited dimensions makes it possible to avoid an flow of cooling air passing through the radial air passage from increasing to a lager extent, thereby having less influence on an amount of cooling air taken in through the axial opening. As a result of it, an amount of cooling air for the smaller-diameter fin and the rectifying elements mounted thereon will not be reduced so much, gaining a preferable cooling performance.
Also preferably, each groove on the radial air passage has a height in the axial direction, said height being set to an amount equal to or larger than about 0.5 times of a thickness of the larger-diameter fin.
This setting of dimensions is able to provide a sufficient amount of air to cooling air circulating along a predetermined portion in the radial air passage, the predetermined portion being by the rear of the larger-diameter fin and being opposed to positions of the rectifying elements mounted on the front of the larger-diameter fin. Thus it is possible to steadily cool down the larger-diameter fin and the rectifying elements mounted thereon.